The CLARA FEL Test Facility on behalf of the CLARA Project Team Jim Clarke STFC Daresbury Laboratory and The Cockcroft Institute on behalf of the CLARA Project Team

Free Electron Lasers FELs have made huge advances in the past few years First X-ray FEL in 2009 (LCLS) then SACLA in 2011 More X-ray facilities are under construction Advanced soft X-ray facilities are also now operating routinely for users as well (FLASH & FERMI) The potential for improvements is enormous Better temporal coherence Better wavelength stability More power Better intensity stability Ultra-short pulses of light Two-colour or Multi-colour output …

The ‘FEL Case’ for an FEL Test Facility Free-Electron Lasers (FELs) are remarkable scientific tools Short-wavelength FELs are operating for users around the world, for example LCLS (USA), SACLA (Japan), FLASH (Germany) and FERMI@Elettra (Italy). There are still many ways their output could be improved: Shorter Pulses Improved Temporal Coherence Tailored Pulse Structures Stability & Power There are many ideas for achieving these aims, but many of these ideas are untested Beamtime on FELs is over subscribed by users and so little time for R&D

CLARA Compact Linear Accelerator for Research and Applications The CLARA Concept There are many ways FELs can be improved, but limited scope with existing facilities UK Scientists need FELs and we want to develop next generation FEL technology towards a possible UK facility CLARA Compact Linear Accelerator for Research and Applications An upgrade of the existing VELA Photoinjector Facility at Daresbury Laboratory to a 250MeV Free-Electron Laser Test Facility Proof-of-principle demonstrations of novel FEL concepts Emphasis is ULTRA-SHORT PULSE GENERATION Strathclyde INFN Frascati SwissFEL DLS Oxford Liverpool Imperial

Other Goals and Benefits of CLARA CERN FERMI@Elettra RHUL INFN Frascati SwissFEL DLS Lancaster INR Moscow The opportunity for R&D on advanced technologies: New photoinjector technologies Novel undulators (short period, cryogenic, superconducting….) New accelerating structures: X-Band etc... Single bunch diagnostics. The enhancement of VELA beam power and repetition rate, enabling additional industrial applications. The possibility to use the electron beam for other scientific research applications: COMPTON SCATTERING FOR GAMMA BEAMS PLASMA ACCELERATOR RESEARCH ULTRAFAST ELECTRON DIFFRACTION DIELECTRIC WAKEFIELD ACCELERATION NOVEL TYPES OF STORAGE RING Strathclyde Manchester INFN Frascati York Swansea UCL

Design Philosophy and Parameters CLARA will be a flexible test facility allowing the broad range of accelerator and FEL R&D necessary to ensure a future UK FEL facility is world leading. Many of the FEL research topics are in two main areas which are intended to demonstrate improvement of FEL output beyond that available from SASE The generation of ultra-short pulses Our emphasis for the short pulse schemes is to generate pulses with as few optical cycles as possible with durations of the order of, or shorter than, the FEL cooperation length. For these schemes we will lase at 400–250 nm, where suitable nonlinear materials for single shot pulse profile characterisation are available. A suitable wavelength range for seed sources to manipulate the electron beam longitudinal phase space is 30 – 120 um Improvement of temporal coherence. For these schemes we will lase at 266-100nm because here only spectral characterisation is required. A suitable seed source for harmonic upconversion, if required, is an 800nm Ti:S. In all cases, we aim to study the essential physics of the schemes which can often be independent of the FEL wavelength. Using a hybrid planar undulator, with minimum gap 6mm, and gap tuning range of 400–100 nm, the required electron beam energy is ~230 MeV.

INTERACTIONS WITH LASER BEAMS CLARA Layout FEL OUTPUT STUDIED PLASMA TEST LINE FEL OUTPUT GENERATED The existing VELA RF Photoinjector Facility INTERACTIONS WITH LASER BEAMS ELECTRONS ACCELERATED AND MANIPULATED ELECTRONS GENERATED HERE

FEL Layout + Operating Modes 7 x 1.5m RADIATORS, 27mm PERIOD, ON-AXIS FIELD HORIZONTAL 1.1m GAPS, with QUAD, BPM, SCREEN + DELAY CHICANE Seeding Mode is for Short Pulse Schemes FEL lasing: 400-250nm (Seed: 30-120µm) + Temporal Coherence Schemes FEL lasing: 266-100nm (Seed: 800nm)

Short Pulse Schemes: Sliced Chirped Beam + Taper* Principle of scheme Few-cycle laser interacts with electron beam to generate strong energy chirp in short region of bunch Radiator taper is matched to energy chirp to maintain resonance as FEL pulse slips forwards to electrons with different energies FEL gain strongly suppressed in remainder of bunch Constraints Length of chirp needs to match cooperation length for single SASE spike to grow Amplitude of chirp needs to be greater than natural bandwidth of FEL * E. Saldin et al., PRST-AB. 9, 050702, (2006) Slide courtesy Ian Martin, DLS

CLARA Short Pulse Schemes: Predicted Pulse Durations Typical SASE output is ~100,000 cycles

Temporal Coherence: High-Brightness (HB) SASE* As in the mode-coupled FEL, delays are used between undulator modules Each delay is different to prohibit growth of modes Increased slippage gives increased communication length between radiation and electrons, delocalising the collective FEL interaction and allowing coherence length to grow exponentially by up to 2 orders of magnitude (compared to SASE) In contrast to other schemes for improving temporal coherence: No seed laser or photon optics are required It’s all done with magnets, and is thus applicable at Any Repetition Rate and Any Wavelength. Was demonstrated (over a limited parameter range) on LCLS, using detuned undulators as delays, and shown to reduce linewidth in inverse proportion to the increased slippage – can’t test optimum scheme * B. W. J. McNeil, N. R. Thompson & D. J. Dunning, Transform-Limited X-Ray Pulse Generation from a High-Brightness SASE FEL, PRL 110, 134802 (2013)

Temporal Coherence: HB-SASE 100nm HB-SASE on CLARA, CDR lattice SASE HB-SASE Four different shots on CLARA demonstrate variability of SASE & advantage of HB-SASE

CLARA Status The CDR was published in July 2013 The project has now been split into Two Phases PHASE 1 – Front End, 50 MeV This is happening now, with procurement progressing, and installation in 2015. Will enable access to bright, short, up to ~50 MeV electron bunches for UK accelerator science and technology community Will enable new high rep rate photoinjector to be characterised with beam whilst VELA/CLARA Phase 1 still operational (i.e. two guns) Potential for early exploitation of 20 TW laser PHASE 2a – 150 MeV section Funded, procurement starting this year SwissFEL are providing 3 linacs, together with a number of quadrupoles and solenoids (available Q4 2014) PHASE 2b – 250 MeV FEL Test Facility Not Yet Funded – Part of Ongoing UK Capital Consultation Exercise

VELA + CLARA Phase 1 (2015) ~50MeV ~50MeV ~50MeV ~5 MeV ~ 5 MeV

Summary CLARA is a proposed FEL test facility for the UK NC RF (up to 400 Hz) Emphasis on ultra short pulse generation Enabling other electron beam applications Major upgrade to VELA CLARA Phase 1 (Front End) is due for installation in 2015 Phase 2 partially funded already Many active collaborations already with leading UK and European accelerator and FEL teams UK FEL aspiration of hard X-rays implies NC RF selection CLARA ideally suited to carry out technology tests and effectively duplicates front section of multi-GeV accelerator